There are many applications that require some sort of confirmation to a system that sensors have been placed properly on objects for different purposes, such as sensing, monitoring, measuring or diagnosing. For example, temperature sensors, such as thermocouples or thermistors, may be placed on an internal combustion engine to provide a thermal mapping of the engine. Biosensors, such as pulse sensors, blood pressure sensors, CO2 sensors, etc., may be placed on a patient to monitor various activities, such as heart function, breathing, perspiration, etc.
One important example of a medical application that requires placing sensors on objects and which takes into account the spatial position of the sensor or of some landmark location (e.g., some anatomical part) is that of monitoring the progress of labor during childbirth. Applicant's U.S. Pat. No. 6,200,279, entitled “Method And Apparatus For Monitoring The Progress Of Labor”, describes such an application. Briefly, in one of the methods described in U.S. Pat. No. 6,200,279, a position sensor is attached to a predetermined point on the mother's pelvic bones, and the location of the position sensor in three-dimensional space is monitored relative to a reference. The location of a fetal presenting part (e.g., the tip or the bi-parietal diameter (BPD) of the fetal head) may be monitored with respect to the predetermined point on the mother's pelvic bones to provide an indication of the progress of labor. Not only may position sensors be used to monitor the location of the fetal presenting part, but they may also be used to monitor the position of the sides of the mother's uterine cervix.
If more than one sensor is used, it is readily understood that each sensor must be properly identified. Various methods are known in the art for identifying the abovementioned sensors. For example, independent external verification signals have been used to identify sensors.